Fire Suppression Types

Wet Pipe Systems

By a wide margin, wet pipe sprinkler systems are installed more often than all other types of fire sprinkler systems. They also are the most reliable, because they are simple, with the only operating components being the automatic sprinklers and (commonly, but not always) the automatic alarm check valve. An automatic water supply provides water under pressure to the system piping. All of the piping is filled with water. Until sufficient heat is applied, causing one or more sprinklers to fuse (open), the automatic sprinklers prevent the water from being discharged.

DRY PIPE SYSTEMS

Dry pipe systems can only be used (by regulation) in spaces in which the ambient temperature may be cold enough to freeze the water in a wet pipe system, rendering the system inoperable. Dry pipe systems are most often used in unheated buildings, in outside canopies attached to heated buildings — in which a wet pipe system would be provided — or in refrigerated coolers. Dry pipe systems are the second most common sprinkler system type.

Water is not present in the piping until the system operates. The piping is pressurized with air, at a “maintenance” pressure which is relatively low compared with the water supply pressure. To prevent the larger water supply pressure from forcing water into the piping, the design of the dry pipe valve (a specialized type of check valve) intentionally includes a larger valve clapper area exposed to the maintenance air pressure, as compared to the water pressure.

DELUGE SYSTEMS

“Deluge” systems are systems that have open sprinklers (i.e. the heat sensing operating element is removed during installation), so that all sprinklers connected to the water piping system are open. These systems are used for special hazards where rapid fire spread is a concern, as they provide a simultaneous application of water over the entire hazard.

Water is not present in the piping until the system operates. Because the sprinkler orifices are open, the piping is at an ambient air pressure. To prevent the water supply pressure from forcing water into the piping, a deluge valve is used in the water supply connection, which is a mechanically latched valve. It is a non-resetting valve, and stays open once tripped.

Because the heat-sensing elements present in the automatic sprinklers have been removed (resulting in open sprinklers), the deluge valve must be opened as signalled by a specialized fire alarm system. The type of fire alarm initiating device is selected mainly based on the hazard (e.g., smoke detectors, heat detectors, or optical flame detection). The initiation device signals the fire alarm panel, which in turn signals the deluge valve to open. Activation can also be manual, depending on the system goals. Manual activation is usually via an electric or pneumatic fire alarm pull station, which signals the fire alarm panel, which in turn signals the deluge valve to open.

Operation

Activation of a fire alarm-initiating device, or a manual pull station, signals the fire alarm panel, which in turn signals the deluge valve to open, allowing water to enter the piping system. Water flows from all sprinklers simultaneously.

A deluge system may be required in a risk area where fire may be expected to spread quicker than the progressive operation of normal sprinkler heads.

Pre-Action Systems

BPre-action sprinkler systems are specialized for use in locations where accidental activation is undesired, such as in museums with rare art works, manuscripts or books.

Pre-action systems are hybrids of wet, dry and deluge systems, depending on the exact goal of the system. There are two sub-types of pre-action systems: single interlock, and double interlock. The operation of single-interlock systems are similar to dry systems except that these systems require a “preceding” and supervised event (typically the activation of a heat or smoke detector) to precede the “action” of water introduction into the system’s piping due to opening of the pre-action valve (which is a mechanically latched valve). Once the fire is detected by the fire alarm system, the system is essentially converted from a dry system into a wet system. Or, if an automatic sprinkler operated prior to the fire being detected by the fire alarm system, water will be allowed into the piping, and will discharge water from the sprinkler.

Operation

The operation of double-interlock systems is similar to deluge systems except that automatic sprinklers are used. These systems require that both a “preceding” and supervised event (typically the activation of a heat or smoke detector), and an automatic sprinkler activation take place prior to the “action” of water introduction into the system’s piping. There is also a little-used variation known as non-interlock.

Carbon Dioxide Systems

Carbon dioxide is a clean, non-corrosive, non-flammable gas which extinguishes fire by diluting flammable mixtures of air and gas or vapour to proportions below their flammable or explosive limits. It is especially valuable where other extinguishing mediums might damage stock or equipment.

Carbon dioxide-based systems are suitable for electrical rooms, boiler rooms, transformers and other sensitive areas.

Foam Systems

There are a variety of effective fire-fighting foams in use today. These are made from liquid concentrates and are referred to as mechanical or air foam.

Clean Agent Gas Systems

FM 200, Inergen®, and Novec™ 1230 are all clean agent gas systems that are a direct replacement to Halon 1301 (bromotrifluoromethane). Each of these gas systems is a clean, non-corrosive gas, which is designed to extinguish fire. All are especially valuable where other extinguishing media might damage stock or valuable equipment. These systems are used most often in computer, electrical and telecommunication equipment rooms.

A description of each, and how they differ, is as follows:

FM 200 Systems

Extinguishes Class A, B, and C fires by interrupting the chemical chain reaction. It also absorbs heat, thus accelerating the suppression process. This gas is safe to use in occupied spaces at concentrations up to 9% by volume. FM 200 will not deplete stratospheric ozone and it has a relatively short atmospheric lifetime of 31-42 years.

FM 200 is suitable for a central computer room, a room which stores important documents or areas that store similarly valuable items.

Novec™ 1230 Systems

Designed by 3M™, Novec™ 1230 fluid works as a gas, yet it is a liquid at room temperature. Novec™ is used to extinguish Class A, B and C fires via its cooling effects. This agent extinguishes fires at concentrations of 4-6% by volume and thus it offers the largest safety margin of any chemical clean agents for occupied spaces.

Inergen® Systems

Extinguishes Class A, B and C fires by removing enough oxygen from the air to break the fire chain, yet still allows people to breathe comfortably. For Class A and B fires, the speeds of extinguishment have occurred in as little as 22 and 17 seconds, respectively. Inergen® is completely environmentally friendly and is composed of naturally-occurring gases already found in the air we breathe. It has zero ozone depletion, global warming and atmospheric lifetime potential.

Water Mist Systems

If water damage or water volume is of particular concern, a technique called water mist fire suppression may be an alternative. This technology has been under development for over 50 years. It hasn’t entered general use, but is gaining some acceptance on ships and in a few residential applications. Mist suppression systems work by lowering the temperature of a burning area through evaporation rather than “soaking.” As such, they may be designed to only slow the spread of a fire and not extinguish it. Some tests — that may or may not be biased — showed the cost of resulting fire and water damage with such a system installed to be dramatically less than conventional sprinkler systems.